KOLKATA
: Two IndiGo planes came too close for comfort before averting a mid-air collision on October 31 at the border airspace of Bangladesh and India, Airports Authority of India (AAI) officials said.

With only 45 seconds before the possible collision, it was averted after the Air Traffic Control (ATC) tower in Kolkata instructed one plane to turn right and move away from the other aircraft that had come at the same level.

"Both the aircraft, belonging to low cost carrier IndiGo, had come on the same level on Wednesday evening and posed a threat to both the aeroplanes," a senior AAI official said at the Kolkata airport.

One aircraft was going to Guwahati from Chennai and the other from Guwahati to Kolkata. The Kolkata-bound flight was at 36,000 ft in Bangladesh airspace and the other one at 35,000 ft in Indian airspace.

The Hazrat Shahjalal International Airport, Dhaka’s ATC had asked the Kolkata-bound flight to descend to 35,000 ft and when the aircraft followed the order, it came close to the aircraft which was at 35,000 ft.

An ATC official in Kolkata saw it and immediately ordered the Chennai-Guwahati flight to make a right turn and move away from the path of the descending aircraft, averting a disaster, he said.

It is not known if the Airborne Collision Avoidance System (ACAS) or the Traffic Alert and Collision Avoidance System (TCAS), which are generally built-in equipment in new aircrafts, had alerted the pilots or not, the official said, adding that everything will be found out during the investigation.

As per rule, the standard separation gap between two aircraft, both vertical difference and lateral difference, should be a minimum of 1000 ft, said sources at the airport.

Earlier in May 2 another IndiGo, Air Deccan planes averted a mid-air mishap over Dhaka airspace after an automatically generated warning alerted the pilots of IndiGo and Air Deccan planes, which came dangerously close to each other.

The incident happened when IndiGo's Agartala-bound flight 6E892 from Kolkata and Air Deccan's flight DN 602, which was on its way to Kolkata from Agartala.

The incident has been treated as "serious" as IndiGo Airbus A320 plane and Air Deccan's Beechcraft 1900D were just about 700 metres away.